Can birth weight and gestational age at delivery of singleton gestational carrier pregnancies be predicted by the gestational carrier’s own previous singleton pregnancies?

Abstract

Gestational carriers (GC) represent a unique population in which to study the effect of assisted reproductive technology on obstetric outcomes, as they are not infertile and have usually had favorable obstetric outcomes in the past. In GC pregnancies, important questions remain regarding how perinatal outcomes are differentially impacted by the genetic parents versus the GC. This study sought to compare birth weight and gestational age at delivery between a GC’s prior own pregnancies versus the current GC pregnancy. A retrospective analysis of all GC singleton deliveries from a single agency between 2008-2019. Data from a large surrogate agency that consisted of matched GCs and intended parent couples for an index GC pregnancy were reviewed. GCs with a history of or current multiple gestation as well as with a history of or current preterm delivery were excluded. All available birth weights of the GCs own children as well as the gestational age at delivery for the GC’s last own birth were collected. Both average birth weight and last singleton birth weight of the GC’s prior own deliveries were correlated to the birth weight of the index GC pregnancy. Gestational age at delivery of the GC’s last own delivery was compared to the gestational age at delivery for the index GC pregnancy. Of 836 GCs, 101 were eligible for inclusion in this study. Average age of GCs at time of delivery was 34.9 years (SD 4.4) and their average BMI was 24.3 (SD 3.13). 93 GCs (76.9%) had a prior parity of ≥3, and 27 (22.3%) had grand multiparity (≥5). The average birth weight of all GC’s prior spontaneously conceived singletons was 7.83 lbs (SD 3.01) and 7.68 lbs (SD 1.01) for the GC’s most recent own singleton delivery. Average BW of index GC pregnancies was 7.62 pounds (SD 1.05). While average birth weight of all the GC’s prior singleton children was not correlated with the birth weight of the index GC pregnancy (r=0.051, P = 0.623), the birth weight of the GC’s most recent own singleton birth was significantly correlated with the birth weight of the index GC pregnancy (r=0.298, P = 0.003). Birth weight of the index GC pregnancy was not correlated with GC BMI (r = 0.083, P = 0.423). Mean gestational age at delivery was similar between the GC’s last own singleton delivery and the index GC pregnancies (mean 39.1 (SD 0.993) vs. 39.1 (SD=0.983), P<0.001). Gestational age at delivery of the GC’s last own singleton pregnancy was also significantly associated with the gestational age at delivery for the index GC pregnancy (P<0.001). While birth weight and gestational age at delivery are likely multifactorial and impacted by both genetic and environmental factors, we found that in singleton GC pregnancies birth weight and gestational age are correlated with birth weight and gestational age of a GC’s last own delivery.This data is of value when counseling both intended parents and evaluating candidacy for potential surrogacy.